For example, air filters are used in the air supply of internal combustion engines in order to remove pollutants and dirt particles from the air supplied for the combustion so that only purified air is supplied to a combustion process in the internal combustion engine.
An air filter has an inflow opening for unpurified, dirty air and an outflow opening for the filtered, clean air; the filter element performs the actual filtering function. The air supply of the internal combustion engine is provided via the outflow opening of the air filter; the internal combustion engine takes in the required air or air quantity. The filter element or air filter element is composed of a filter medium such as a filter paper through which the air that is to be filtered flows when the internal combustion engine sucks air in so that the dirt particles contained in the air flowing through are separated or removed in the filter medium.
Usually, the filter medium is folded (folded filter) or has a multitude of filter chambers (fluted filter) in order to increase the surface area of the filter, which also extends the service life of an air filter element since a larger filter surface area can absorb more dirt particles before the pressure drop at the filter medium caused by separated dust has become so significant that the air is no longer allowed to pass through to the internal combustion engine in the required quantity and the air can no longer pass or flow through the filter medium.
Usually, the filter element is contained in the housing and, for example, a functional element in the form of an additional filter element is provided in the housing, upstream of the outflow opening of the air filter. The additional filter element in this case performs the function of preventing dirty air from flowing into the internal combustion engine through the air filter, even if the air filter has been removed from the housing. For this reason, a main element or air filter element and a functional component must usually be placed inside the housing of the air filter.
In addition, the structural design of the housing can be adapted to external circumstances, e.g. the spatial circumstances inside the engine compartment of a motor vehicle. The structural design of the housing has a direct influence on the size of the air filter element and therefore on the filtration performance of the air filter element.
Depending on the volume inside the air filter housing occupied by the functional component, the main element or air filter element is correspondingly reduced in size and/or the depth of the air filter folds or filter chambers of the main element is adapted so as to divide up space inside the air filter housing.
Usually, the folds of the filter element are folded or the depths of the filter chambers are embodied so that they are equal in depth and thus constitute a block-shaped air filter element. This can, however, result in the fact that the functional component does not take up the entire space that the block-shaped design of the main element leaves open on the inside of the housing.
WO 98/47601 has disclosed a filter element in the form of a folded filter element for an air filter; the filter element is composed of a filter insert embodied in zigzag form.